There are a wide range of analytical operations that may be benefited from the ability to analyze the reaction of individual molecules, relatively small numbers of molecules or molecules at relatively low concentrations. A number of approaches have been described for providing these sparsely populated reaction mixtures. For example, in the field of nucleic acid sequence determination, a number of researchers have proposed single molecule, or low concentration approaches to obtaining sequence information in conjunction with the template dependent synthesis of nucleic acids by the action of polymerase enzymes.
The various different approaches to these sequencing technologies offer different methods of monitoring only one or a few synthesis reactions at a time. For example, in some cases, the reaction mixture is apportioned into droplets that include low concentrations of reactants. In other applications, certain reagents are immobilized onto surfaces such that they may be monitored without interference from other reaction components in solution. In still another approach, optical confinement techniques are used to ascertain signal information only from a relatively small number of reactions, e.g., a single molecule, within an optically confined area. Notwithstanding the availability of the above-described techniques, there are instances where further selectivity of reaction components for analysis would be desirable. The present invention meets these and a variety of needs.